David has an identical twin brother, Stephen, who is a child psychiatrist. They went to different schools and once swapped schools for a day. David trained in London, Sydney and Oxford. In 1989 he moved to Sydney to head a Department of Immunology and Infectious Diseases at the Royal Alexandra Hospital for Children, but was the only member of the Department. He is Clinical Professor in Paediatric Infectious Diseases at the Children’s Hospital at Westmead and the University of Sydney. In 2002, he obtained a post-graduate diploma in bioethics from Monash University and since then has supervised medical students in bioethics research projects and published 100 peer-reviewed articles on bioethics. He started the Health Assessment for Refugee Kids (HARK) Refugee Clinic in 2005, which sees over 600 asylum seeker and refugee children a year. In late 2014 he went to Nauru to consult on children and has become a more vocal advocate ever since.